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186. 反转字符串中的单词 II

English Version

题目描述

给你一个字符数组 s ，反转其中 单词 的顺序。

单词 的定义为：单词是一个由非空格字符组成的序列。s 中的单词将会由单个空格分隔。

必须设计并实现 原地 解法来解决此问题，即不分配额外的空间。

 

示例 1：

输入：s = ["t","h","e"," ","s","k","y"," ","i","s"," ","b","l","u","e"]
输出：["b","l","u","e"," ","i","s"," ","s","k","y"," ","t","h","e"]

示例 2：

输入：s = ["a"]
输出：["a"]

 

提示：

• 1 <= s.length <= 105
• s[i] 可以是一个英文字母（大写或小写）、数字、或是空格 ' ' 。
• s 中至少存在一个单词
• s 不含前导或尾随空格
• 题目数据保证：s 中的每个单词都由单个空格分隔

解法

先翻转里面每个单词，最后再将字符串整体翻转。

Python3

class Solution:
    def reverseWords(self, s: List[str]) -> None:
        """
        Do not return anything, modify s in-place instead.
        """

        def reverse(s, i, j):
            while i < j:
                s[i], s[j] = s[j], s[i]
                i += 1
                j -= 1

        i, j, n = 0, 0, len(s)
        while j < n:
            if s[j] == ' ':
                reverse(s, i, j - 1)
                i = j + 1
            elif j == n - 1:
                reverse(s, i, j)
            j += 1
        reverse(s, 0, n - 1)

Java

class Solution {
    public void reverseWords(char[] s) {
        int n = s.length;
        for (int i = 0, j = 0; j < n; ++j) {
            if (s[j] == ' ') {
                reverse(s, i, j - 1);
                i = j + 1;
            } else if (j == n - 1) {
                reverse(s, i, j);
            }
        }
        reverse(s, 0, n - 1);
    }

    private void reverse(char[] s, int i, int j) {
        for (; i < j; ++i, --j) {
            char t = s[i];
            s[i] = s[j];
            s[j] = t;
        }
    }
}

C++

class Solution {
public:
    void reverseWords(vector<char>& s) {
        int n = s.size();
        for (int i = 0, j = 0; j < n; ++j) {
            if (s[j] == ' ') {
                reverse(s, i, j - 1);
                i = j + 1;
            } else if (j == n - 1) {
                reverse(s, i, j);
            }
        }
        reverse(s, 0, n - 1);
    }

    void reverse(vector<char>& s, int i, int j) {
        for (; i < j; ++i, --j) {
            swap(s[i], s[j]);
        }
    }
};

Go

func reverseWords(s []byte) {
	n := len(s)
	for i, j := 0, 0; j < n; j++ {
		if s[j] == ' ' {
			reverse(s, i, j-1)
			i = j + 1
		} else if j == n-1 {
			reverse(s, i, j)
		}
	}
	reverse(s, 0, n-1)
}

func reverse(s []byte, i, j int) {
	for i < j {
		s[i], s[j] = s[j], s[i]
		i++
		j--
	}
}

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